Usually polymer's Molecular weight is express by the suppliers in terms of --###--- (some number) determined by GPC; how to convert this number in to g/mol ?
Yes, the number in Da translates to g/mol. For e.g. if the Mw=50,000Da (or 50kDa) it's equal to 50,000 g/mol.
The number which is expressed by the company (determined by GPC) is actually in Daltons (Da, 1kDa=1000Da). Dalton is actually a very small unit and hence is used to denote unified atomic mass unit (u) which is approximately equal to the mass of a single nucleon (either a proton or neutron). The magnitude of 1Da equals to ~1.66x10^-27kg (which is equal to one twelfth the mass of an unbound neutral carbon-12 atom). Since 1 mole of atoms/molecules refers to Avagadro constant (i.e. 6.022x10^23) of corresponding entities, the weight of 1 mole works out be -> (1.66x10^-27kg)x(6.022x10^23)=1gram (approx).